Automatic telephone-exchange system.



PATENTED JULY 17, 1906.

A. M. BULLARD.

AUTOMATIC TELEPHONE EXCHANGE SYSTEM.

APPLICATION mum OCT. 16. 1905.

ms Non/4's Vslss's co., WASnlucroN. m c,

a 8 .m n m M. r we .v..

PATENTED JULY 1'7, 1906.

A. M. BULLARD. AUTOMATIC TELEPHONE EXCHANGE SYSTEM.

[I ll llll ill Z pirwss) as:

No. 826,310. PATENTBD JULY 17, 1906. A. M. BULLARD.

AUTOMATIC TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED 001210. 1005.

4 SHEETSSHBET 3.

No. 826,310. PATENTED JULY 17, 1906.

A. M. BULLARD.

AUTOMATIC TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED 0GT.16, 1905.

4 SHEETS-SHEET 4.

frame/0Z0)? UNITED STATES PATENT oFFioE.

ALBERT M. BULLARD, OF NEW YORK, N. Y., ASSIGNOR TO WESTERN w ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A' CORPORATION OF ILLINOIS.

To (1,35 whom it may concern.-

Be it known that I, ALBERT M. BULLARD, a citizen of the United States, residing at New York, in the county of New York and State ofNew York, have invented a certain new and useful Improvement in Automatic Telephone-Exchange Systems, of which the folowing is a full, clear, concise, and exact description.

My invention relates to an automatic tele phone-exchange system; and its object is to provide an improved. organization of circuits and a paratus by which the selective switching any two subscribers instruments into connection with each other may be accomplished rapidly and with certainty, while meeting the various requirements of signaling, prevention of interference with busy lines, including both testing and lock-out features, good telephone transm1ssion,economy of current consumption, and simplic- Fig. 2 is a plan view of the selector-switch ity and cheapness of the apparatus, which are all essential to a thoroughly practicable system.

The invention has particular reference to such exchanges as are limited to a comparatively small number of subscribers circuits say a hundredsome or all of which maybe party-lines having several subscribers instruments connected thereto, although certain features of the invention may be employed with advantage in larger exchanges.

The accompanying drawings illustrate an automatic telephone-exchange system wh1ch is typical of my invention, and I will describe that system in detail, reserving for the concludin claims a more general statement as to the eatures, improvements, or combinations believed to be novel.

Figure is a circuit diagram of two telephone-lines extending from their respective subscribers stations to a central office, where each line is equipped with apparatus for performing the various switching operations required in making connection with any other line of the exchange, it being understood that each line of the exchange has an equipment similar to that of the lines shown in Fig. 1.

which is rovided for each line at the central ofiice. or a hundredline exchange one hundred of these selectors would be 're- Specification of Letters Patent.

Application filed October 16, 1905. Serial No. 283.022.

AUTOMATIC TELEPHONE-EXCHANGE SYSTEM.

Patented July 17, 1906.

tral-battery plan both for signalin n y; two main'con r x.

ing. Each line has, as usua I ductors or line-wires 1 2, and the central battery I) is connected in a bridge of theicir- I I cuit, the ne ative pole of said battery,-with which con uctor 1 is connected, being f I grounded in accordance with the usual prac- H tice. A ringing-relay a is connected inthebridge between the grounded pole of the battery and conductor 1, and a selecting-relay c is also connected in the brid e between the free-pole of the battery an conductor 27 5 The line-wires 1 and 2 are extended through separable contacts controlled by the selector of that line to multiple incoming call ter'minal pieces or contacts g on al the other" selectors, so that each c has a air of terminals on each selector at which t e movable contacts of the selector mayni'a'ke connection therewith. Each selector is provided with a rotating arm f, arranged to be ad--' vanced by a stepping magnet e and to be held in its advanced position by a retainingmagnet (1, said magnets being'connected in a local circuit 5 6 7, which is controlled by'the selecting-relay c, said relay in turn being controlled by the switchin mechanism at the subscribers station. The selector-arm f is provided with two contactbrushes or wipers f f which are arranged to trail over the pairs of stationary line-terminals h h ,arranged in a circle about its axis. Thecon- 5 tact-brush f of the selector-arm is arranged to be connected by a conductor 3 with the line conductor 1, of which it forms an extension, said conductor 3 being conductively divided by a condenser. y and being normally mo o en at contacts of the rin ing-relay a and a s ow-acting relay k. Simi arly the contact: brush f 2 of the selector-arm is arranged tobe connected with line conductor 2 by an ex quired. Fig. 3 is aside elevation of'the setension 4 of said conductor, said extension being .also normally open at other contacts of the slow-acting relay 7c.

The selector-arm carries an insulating-stud 5 f", which when said arm is in its idle position serves to,maintain a pair of contact-springs l I under tension in engagement with corresponding contact-anvils to extend the circuit o the line conductors 1 2 to the several pairs of multiple contact-terminals g g for incomin calls on the other selectors.

ormally the line conductors 1 2 are thus extended (conductor2 through a condenserm) to their incoming call terminals g 9 but when the selector-arm is advanced such normal connections are broken at the sprin s Z 1 and when relays a, and k are excited tfie line conductors are connected by extensions 3 and 4 with the selector-arm contact-brushes 20 f f, respectively, and by said brushes to the terminals h k of the called line.

. Each selector of a party-line is rovided with one pair of terminal pieces k L to represent its own line for reverting callsthat is to say, for calls from one subscriber's station to another subscribers station on the same line. The terminal h of this pair is connected directly to line conductor 1, while terminal piece It is simply a dummy, having no electrical connection.

Subscribers stat/ion equipment-As before stated, the advance of the selector-arm at the central ofiice is dependent upon the intermittent closing of the local circuit 5 6 7, which is controlled at a normally open contact of the selecting-relay c. To roduce an intermittent excitation of this re ay 0, the subscriber s station equipment includes, in addition to the usual telephone apparatus, an interrupter n, which when operated will open the metallic circuit and intermittently connect the line conductor 2 to earth by way of a contact 0 of the telephone-hook. The interrupter comprises a toothed wheel n, meshing with a pinion, arranged to actuate a contact n as the teeth of the wheel pass in succession under a movable spring. A ratchet-wheel n is mounted to rotate with the toothed Wheel n, and the controller-arm n, which may be moved forward loosely upon the axis of the wheel against the tension of a coiled spring a, carries a pawl a which as the controllerarm is returned by the spring after its advance engages the ratchet-wheel to carry the same and the toothed wheel 11. around with it, whereby the contact a is made and broken a certain number of times, dependent upon the distance to which the controller-arm has been advanced. The substation equipment also includes a ringing-key p, which is adapted to open the metallic circuit and connect the line conductor 2 through normally closed contacts n n of the interrupter mechanism and contact 0 of the switch-hook to earth. While the interrupter is in operation, contacts 727 n are open, and premature manipulation of the ringin key will have no effect.

Mes anism for rotating the selector-arm.- The selectorarm is fastened radially upon a ratchet-wheelf, which is mounted to rotate in a suitable frame. The contact-brush f 2 is in electrical connection with said selectorarm f and with the metallic mounting or frame, while the other contact-brushf, carried by the selector-arm, is insulated therefrom and connected with a metallic strap f extending along the top of the arm to the axis of rotation thereof, at which point a contact-spring f makes continuous contact therewith. Said contact-spring f 5 is connected to conductor 3. The stepping-magnet e is provided with an armature e, which carries a pawl 6 adapted to enga e the teeth of the ratchet-wheel f When the armature is at tracted, the pawl advances the ratchet-wheel and the selector-arm is carried thereby one step. The ratchet-wheel is arranged to be held at any point to which it may be advanced by a retaining-pawl d governed by the armature d of the retaining-magnet d. When the armature d is in its normal position, it holds the retainingpawl (1 out of engagement with the ratchet-wheel but when said armature is attracted the retaining-pawl is pushed against the ratchet-wheel by a spring. The cooperation of both the stepping-magnet and the retaining-magnet is thus necessary to bring about the rotation of the selector-arm. The retaining-magnet is arranged to act sluggishly in releasing by means of a non-inductive shunt d and by having a small air-gap between its poles and the armature, while the stepping magnet is adapted by contrary arrangements to respond quickly to a cessation of current. These two magnets d and e are in series in the local circuit 5 6 7, and when a pulsating or intermittent current is passed through the circuit the armature d will be continuously attracted, while armature e is vibrated. The

result is a step-by-step advance of the ratchetwheel and t 1e selector-arm carried thereby, the number of steps of advance being determined by the number of impulses of current applied to the magnets. The sluggish relay 7c is also included in the local circuit 5 6 7, with the stepping and retaining magnets e and d; but this relay is normally short-circuited by a conductor 8, which is controlled at normally closed contacts of the ringingrelay (1. and also of said relay k itself. The ringing-relay being inert during the operation of the interrupter n at the subscribers station, the sluggish relay will not be excited until the selecting operation has been com pleted. When the sluggish relay is is once excited, it holds the short circuit 8 open. A short circuit 9 of the stepping-ma net is arranged to be closed by contacts 0 the sluggish relay is when the same is excited. This of ringing-relay a with the conductor 3, which leads through a normally open contact of the sluggish relay k to the contact-brush f of the selector-arm. The continuity of conductor 10 is normally broken at a contact of the selecting-relay c, which contact is closed when the relay is excited. In order that ringing-current may be applied to the brush f of the selector-arm and so to the called line, the relays k and 0 must therefore be excited and the relay a must be inert. Such a condition is brought about when after the selecting operation at the end of which the sluggish relay is has been excited the ringing-key p is actuated at the substation, said key serving to complete the circuit of the selectingrelay 0 to earth while holding the. circuit of the ringing-relay a open.

Busytest and lock-out mechanism.The system is provided with means for automatically notifying a calling subscriber when the line called for is already engaged and for preventing interference with an engaged line. A test-relay t has its magnet provided with an initial exciting-winding t and a lockingwinding t The relay t is adapted when excited to connect line conductor 2 to a conductor 12, leading to the free pole of a grounded battery through the secondary winding M of a busy-tone induction-coil u and also to break the local selector-circuit 5 6 7 to deenergize magnets d and e and permit the selector-arm to return to normal position. The relay 15, when excited, also closes a locking-circuit 5 14, including the magnet-winding t said locking-circuit being controlled at contacts of selecting-relay c, which are closed when said selecting-relay is excited. The source of busy-tone current u is also arranged to be connected by a conductor 13 with the several contacts 9 of the incoming call terminals by way of an alternate contact of the switch-spring Z of the selector. The busytest contact of spring I is closed when the selector-arm is off its normal position, so that at all such times the incoming call terminals 9 g of the line are in connection with the.

free pole of the battery I) through the secondary winding of the induction-coil which produces the busy tone.

Operation of the System.

circuit is completed through his telephone apparatus, and the two polarized relays a and c at the central oflice both attract their armatures, the relay 0 closing the local circuit 5 6 7, and so causing the magnets d and e to advance the selector-arm one. step. This movement effects no chan e in the talking-circuits, being merely inci ental. The subscriber now turns to his interrupter n, inserts a peg in the hole representing the desired line and rotates the controller-arm n until it is stopped by the peg. This movement separates the contact-springs to break the metallic circuit and connect the normally open interruptercontact n to the line conductor 2. When the controller-arm n is released, it begins to return under the influence of a spring, the return movement being retarded by an escapement. The interrupter-wheel n is thus caused alternately to close and open the interrupter-springs, whereby an intermittent current is caused to flow from the central battery I) through the selecting-relay a over the line conductor to earth by way of contact 0 of the subscribers switch-hook. The armature of the selecting-relay c is thus caused to vibrate in unison with the pulsations of current controlled by the interrupter and so causes corresponding intermittent impulses to be transmitted over the local circuit 5 6 7, governing the selector. The ste ping magnet. e is thus caused to intermittent y attract its armature and so to advance the selector-arm step by step. The selector-arm is held in its advanced position by the retainingpawl d controlled by the retaining-magnet,

which being made sluggish does not follow the pulsations of the current, but keeps its armature steadily attracted. Just before the controller-arm of the substation device reaches its normal resting position its rotary-movement contact-springs arerestored to normal condition, which results in a restoration of the metallic circuit through the telephone apparatus and an interruption of the lead to ground. The restoration of the metallic circuit brings about the energization of the ringing-relay a, which was inert during the selective operation and whose armature in its backward position closed the short circuit 8 around the sluggish relay is. When the ringing-relay a is excited, the short circuit is removed from the slow-acting relay is, which, if the called line is not engaged, attracts its armatures with the following results, first, the stepping magnet e is short-circuited by conductor 9, thus preventing further advance of the selectorarm; second, the talking-circuit is extended by conductors 3 and 4 to the selector contact-brushes f f res ectively, and so to the called line, and, thir another break is introduced in the short circuit 8 of the sluggish relay at a back contact of said relay, so that when during the ringing operation, presently to be described, the ringingrelay releases its armatures the sluggish relay will not be again short-circuited. The subscriber now presses his ringing-key p, which grounds the line conductor 2, and then opens the metallic circuit. The selectingrelay 0 is thus maintained excited while the ringing-relay is denergized. The source of ringing-current G, which is positive pulsating current is thus connected by conductors 10 and 3 .to the selector contact-brush f. Current then passes to contact h of the calledsubscribers line out to the called station through the bridge containing the signalbell and back to ground, partly through the selecting-relay of-the called-subscribers line, but mainly through the non-inductive resistance c, bridged upon that relay through one of its back contacts. When the called subscriber answers, there is established a comound talking-circuit comprising bridged impedances a a and c c and interconnecting condensers m y.

Calling an engaged line.The subscriber proceeds as before, and the selector-springs arrive at the terminals of the desired but engaged line. The test side k of the line-terminals h h of an engaged calling-line is put in connection with the free pole of the central battery b by the conductor 13 of such line, while the corresponding terminal h of the engaged line is dead, being separated from battery at the contacts I of such line. The nick-acting test-relay magnet during the se ecting operation has its winding t connected in a path 4 11 to ground from the testing contact-brushf of the selector, said path being normally open at a front contact of the ringing-relay. When the selector-arm has arrived at the terminal of the desired line, and the metallic circuit is restored at the rotary movement springs of the subscribers interrupter, the ringing-relay a attracts its armaturesv much more quickly than does the slug gish relay 7:, so that for an instant the testingcircuit 4 11 is established to earth from the terminal h of the desired line. If there is a potential on this terminal, as where the line is busy, the test-relay t will be excited also before the sluggish relay can respond. When 7 the test-relay is thus excited and draws up its armatures, the conductor 12 is closed to apply busy-tone current to the conductor 2 of the calling-line. Alockingcircuit 14 5 is completed through the other winding of the testrelay to maintain the same excited, and the local circuit 5 6 7, containing the selectormagnets d and e, is broken, so that the selector-arm is released and returns to zero. The busy-tone current from the grounded secondary winding 11, flows through the conductor 12, condenser m, and line-wire 2 to the substation, passing through the bridged telephone apparatus and back over conductor 1 to the grounded pole of the battery I). When the calling subscriber hangs up his telephonereceiver, the local locking-circuit 5 14 is brokeIi at he front contact of the selectin L relay 0, and the apparatus returns to normal condition. If the line called for had been free, there would have been no potential on the multiple terminals W, and the test-relay would not have been excited at the end of the selection, but the sluggish relay k would have been actuated to complete the talkingcircuit, the conductorll, containing the testrelay, being cut off at the same time. The contact-brushes of the selector-arm make wiping contact with the terminals of all lines as said arm advances to the limit of its movement and retires therefrom; but duringsuch movement the said selector brushes are dead or cut off from all circuit connection until the desired line is reached. The-testrelay, furthermore, is kept out of operative relation to the selector until the desired terminal is reached to prevent false tests and lockouts. Summarizing the testing operation, first, at the moment of test the quickacting ringing-relay a, closes the testing-circuit 4 11 through the test-relay t, and the latter, also being quick-acting, promptly draws up its armatures, all before the sluggish relay 7c has time to act. The test-relay in responding deprives the sluggish relay of current, and'a locking-winding on the testrelay keeps the circuits unchanged until the calling subscriber hangs up his telephone. \Vhen a call is transmitted from any line, the incoming call terminals of that line are con nected with the source of test-potential through the spring I of the selector, and when connection is made to a line from some other line test-potential from the central battery is applied to the several multiple terminals of the line to which connection is made by way of the selecting-relay c, conductor 4, and brush-contact h of the calling-line.

Iiaom-ting-calls.A subscriber on a partyline can signal and converse with any other subscriber on the same line. The operation of selection and rin ing is exactly the same as though a subscriber on another linewere being called. The selector contact-brushes are caused to advance to terminals h h, representing the calling-line, of which only the terminal k is used electrically. The ringingselector contact-brush f is brought into contact with said revertive line-terminal b and although connection of the selector with lineconductor 1 is broken at the back contact of spring I it remains established at the revertive contact h. When the ringing-key is pressed after the selecting operation, the ringing-relay armature falls back and closes the ringing-circuit 10 3 to the ringing-selector sprin thence to the revertive line-terminal and conductor 1, from which two paths -to earth are provided'one through the bells and condensers bridged across the line at stations other than that of the calling subscriber to conductor 2 and thence to earth at the shunt being of such resistance that it carthe ringing-key of the calling subscriber, the other through the ringing-relay a to the grounded pole of the battery. The relays a and c are both polarized, and relay 0 is biased in such a way as not to respond to the positive pulsating ringing-current. In calling another substation on the same line or one of the substations on another party-line the calling subscriber rings in accordance with the code-number signal of the station wanted. While two subscribers on the same line are engaged in conversation, their line is busy to other subscribers who may call, because of the advance of the selector-arm from its normal position and the consequent connection of the multiple terminals 9 g to conductor 13 and the busy-tone transformer.

Miscellaneous features-A subscriber under all circumstances is free to operate his selectorthat is, if line A calls line B, line B can disconnect from line A and make any desired selection. hen line B does this, the springs Z Z of line Bs selector are operated, and the busy tone is applied by conductor 13 to the calling-line to notify the calling subscriber of the change. It will be observed that conductor 13 of the called line, including the secondary a of the busy-tone transformer, forms a shunt around the selectingrelay 0 of the calling-line, so that the said secondary winding should have sufficient resistance to prevent the selecting-relay from releasing its arimitures. The interposition of condensers between the line-circuits in addition to other functions permits either subscriber to disconnect or reselect at will. The non-inductive shunt around the selecting-relay c is placed there to keep the relay from being chattered when a line is being signaled,

ries most of the ringing-current from the relay, yet without interfering with its operation by direct current. I will be noted that when the telephone is on the hook at the substation the ground is cut off at contact 0, so that purposeless manipulation of the interrupter-arm or the ringing-key will have no effect on the central-station apparatus. So, also, during the selecting operation before the interrupter-arm has returned to normal position the path to ground controlled by the ringing-key is opened by the rotary-movement springs of the interrupter, so that the actuation of the ringing-key before the selecting operation is completed will have no effect. It will be noted that the ringinglead from the generator at a back contact of the ringing-relay a is normally open at contacts of the selecting-relay c. This provision is to prevent an undesired short rin of the bells on a called line, which would otherwise occur just as the calling subscriber hangs up. The ringing-relay of the calling subscriber releases its armature more quickly than the retaining-magnet can release the selector-arm, and the contact-brush f of the selector would be momentarily connected, through the source of ringin -current, to the back contact of the calling-suiscribers ringin -relay if the ringing-lead were not opene at the same instant by the selectingrelay. I

It will be observed that the apparatus of the substation is the same as that of Patent N 0. 772,023 of October 11, 1904, except that the contact o of the switch-hook has been added to prevent disturbance of the centralstation apparatus during purposeless manipulation of the substation parts while the receiver is'resting on the hook. Also I will mention the fact that there are other forms of selecting apparatus embodying trailinq contacts, quick-acting stepping magnets, anc slow-acting retaining-magnets that are adap ted to be used in my system. I therefore do not confine my claims to the specific details of construction illustrated.

I claim 1. In an automatic telephone-exchange, the combination with a telephone-line, of a selector individual to the lin iaving a movable contact-brush, stationa contact-terminals of other lines, and electromagnetic stepping mechanism-for trailing said contactbrush across said terminals, a selecting-interrupter at the substation arranged to control said electromagnetic mechanism to advance the contact brush to the terminals of a wanted line, a relay is in a local circuit with said stepping mechanism adapted to connect the said contact-brush with the calling-line, a short circuit for said relay, and a switch at the substation actuated in the return of the selecting-intel'rupter to its normal position or in aintaining said short circuit durin the operation of said interrupter, whereby the telephone-line is disconnected from the contact rush of its selector during the selecting operation and then connected with said brush, substantially'as set forth.

2. In an automatic telephone-exchange, the combination with a selector having a movable contact-brush adapted to form the terminal of a calling-line, stationary contacts of other lines with which said movable brush is adapted to be engaged, means for applying test-potential to the stationary contact-terminal of a busy line, a local test-circuit from said movable contact-brush, including the winding of a test-relay, busy-notification apparatus controlled by said testerelay, a selecting-interrupter at the substation, a switch actuated upon the return of said interrupter to its normal position-after the selecting operation, means at the central oflice controlled by said switch for closing the test-circuit, a slow-acting relay k at the central office controlling said test-circuit, said relay 7c bein also controlled throu h the agency of sai substation-switch, sai relay is being adapted IIO when excited to extend the circuit of the calling-line to said movable contact-brush, and means controlled in response to the test-relay for blockin said slow-acting relay, Whereby the movab e contact-brush remains dis-, connected from the calling-line when the called line is busy, but when the called line is not busy the test-relay is cut off in the response of said relay 7:.

3 In an automatic telephone-exchange,

the combination with a telephone-line and a selector therefor comprising a selector switchfirm, a stepping magnet and a retaining-magnet, of a connecting-relay 7c adapted to complete the circuit of the line to the selectorswitch, a selecting-relay c, a ringing-relay a, means for controlling said relays a and c independently or simultaneously from the substation, a local circuit including the stepping magnet, the retaining-magnet and the conmeeting-relay is, controlled by the selectingrelay 0, and a short circuit of the connectingrelay controlled by the rin ing-relay a.

4. In an automatic telephone-exchange, the combination with the selector-switch, the stepping and retaining magnets therefor, a local circuit including said magnets, and means for controlling said circuit from the substation, of a connecting-relay 76 adapted to complete connection of the line through to the selectorswitch, means for exciting said relay controlled at the substation in the selecting-transmitter mechanism, and a short circuit of the stepping magnet established in the response of said connecting-relay.

5. In an automatic telephone-exclnmge, the combination with a telephone-line, ol'- a selector comprising a switch-arm, stepping and retaining magnets and a slow-acting connecting-relay 7c adapted to extend the circuit of the line to the selector-switch, a selecting relay controlling a local circuit through the stepping and retaining magnets and throu h the magnet of connecting-relay 7:, a test-relay t, said relays is and t being each adapted when excited to cut out the other, a ringing-relay a, a test-circuit bringing the test-relay into operative relation to the selector to respond to a test-potential at the terminal of the wanted line, said test-circuit bein closed by the ringing-relay a when excite said relay a being also adapted when excited to break a short circuit normally maintained thereby around the connectingrela and selecting-transmitter mechanism at t e substation adapted first to intermittentl close the circuit of the selecting-relay and finally to close the circuit of both selecting and ringing relays, whereby the selectorarm is advanced by the steppin magnet of the terminal of the wanted line, the circuit of the test-relay is made momentarily effective, and the connection is finally completed upon the response of the relay k if the wanted line is free, or blocked if the test-relay is excited.

6. In an automatic telephone-exchan e, the combination with a telephone-line, of t e selecting andringing relays a and c, and means at the substation for controllin said relays independently and simultaneous y, of the selector comprising a switch, a stepping magnet and a retaining-magnet, a slow-acting connecting-relay and a test-relay arranged to cutout each other when excited, a local circuit including said stepping and retaining magnets and said connecting-relay, controlled by said selecting-relay, a circuit for the test-relay closed by said ringing-relay and a short circuit 8 of the connecting-relay opened by said ringing-relay, when the same is excited, said connecting-relay having contacts adapted when the relay is excited to open said short circuit 8 at another point and to close a short circuit of the stepping magnet, whereby upon the response of said connecting-relay it is maintained excited and the selector-switch maintained stationary under the control of the selecting-relay alone.

7. In an automatic telephone-exchange, the combination with a telephone-line, of a selector comprising connection-terminals for the other telephone-lines and a movable switch-arm carrying brushes adapted to trail over said terminals in the movement of the arm, a stepping magnet adapted when energized to advance said arm, a retaining-magnet adapted to hold said arm in its advanced position, a connecting-magnet controlling the connection of said brushes with the line, a circuit for said magnets, a normally closed shunt about said connecting-magnet, switching mechanism at the substation adapted to ell'ect the intermittent completion of said circuit to cause the stepping magnet to advance the arm to the desired terminals, and means controlled from the substation adapted to open said short circuit after said switcharm reaches the proper terminal.

8. In an automatic telephone-cxchange, the combination with a telephone-line extending in two limbs 1, 2, from a substation to the poles of a grounded source of current, of a switch at the substation controlling the circuit, a relayc at the central office between the free pole of said battery and the line, a selector carrying connection-terminals for each of the other telephone-lines, a movable switch-arm for said selector carrying brushes adapted to trail over said terminals in the movement of the switch-arm, electromagnetic mechanism for advancing said arm, a circuit for said mecl'ianism controlled by relay 0, selective mechanism at the substation adapted to open the line-circuit and intermittently ground the limb of the line connected with the free pole of the battery; whereby the switch-arm may be advanced into engagement with the tern'iinals of any desired line, normally open branches leading trom said limbs 1, 2, to the brushes of said arm, a relay controlling the continuity of said branches, a circuit for said relay, a relay a controlled from the substation adapted to brushes, a magnet for advancing complete said circuit as said brushes reach the'desired connection-terminals, a source of ringing-current, and means controlled at the substation for connecting the same with said branches after the brushes reach the proper terminals.

9. In an automatic tele hone-exchange, the combination with a teiephone-line extending in two limbs 1, 2, from a substation to the poles of a grounded central battery, a.

relay 0 between the free pole of said battery and one limb of the line, a selector carrying connection-terminals for the other tele honelines and a movable switcharm iiaving brushes adapted to engage said terminals in the movement of said arm, normally open branches leading from said limbs 1, 2, to said said arm, a retaining-magnet adapted to ho d the arm in its advanced position, a magnet k controlling the continuity of said branches, a circuit including all of said magnets controlled by relay c, a normally closed shunt around magnet 7c, selective stepby-step mechanism at the substation adapted to first open the linecircuit and successively ground the limb of the line connected with the free pole of the battery, whereby relay 0 makes and breaks the circuit of the stepping magnet to ad vance the switch-arm to the des1red connection-terminal, a relay (1 controlled from the substation adapted, as the switch arm reaches the end of its travel, to break the shunt around relay is, and a shunt around the stepping magnet closed by relay is whenenergized.

10. In an automatic telephone-exchange,

the combination with a telephone-line, a selector at the central office comprising connect1on-termmals for the other lines in the exchange and a movable switch-arm carr ing brushes adapted to engage said termina s, electromagnetic mechanism controlled from the substation adapted to advance said switcharm; whereby said brushes may be brought into engagement with the terminals of any desired line, a sluggish-actin relay controlling the connection of said brushes vwith the line, a circuit for said relay, a switch at the substation adapted to complete said circuit after the switch-arm reaches the proper terminal, a test-relay connected during the test of the called line from earth through contacts controlled by relay is with the switcharm, a grounded source of current associated with each of the other lines, means for connecting the free pole of said battery with the free connection-terminals of any busy line upon the different selectors, a source of toneproducing current adapted to be connected with the calling-line by said test-relay, and normally closed contacts included in the circuit of said sluggish relay controlled by said test-relay; whereby it the line wanted is busy the circuit of the test-relay will be completed to apply the busy-test current to the line and open the circuit of-relay is, but if the called line is free, the relay 7: in connecting the switch-arm with the calling-line will disconnect the test-relay from the switch-arm.

11. In an automatic telephone-exchalwe, the combination with a telephone-line, oi a selector for said line comprising connection terminals for the other lines and a movable switch-arm carrying brushes adapted to onage said terminals, a similar individual seector for each of the other lines, a stepping magnet adapted to advance said switcl1-arm, a retainingmagnet adapted to hold the switch-arm in its advanced position, a circuit for said magnets, mechanism controlled from the substation adapted to successively make and break said circuit to efl'ect the advancement of said switch-arm, a sluggishacting relay 7c controlling the connection of said brushes with the line, a circuit for said magnet, a switch at the substation adapted to com lete said circ lit after the brushes reach the proper terminals, a quick-acting test-relay connected the instant the brushes make connection-With the called line from earth through contacts of relay is with one of the brushes of the switch-arm, a source of grounded current connected with all the corresponding free terminals of a busy line, a source of tone-test current adapted to be connected with the calling-line by said relay when ener ized, normally closed contacts included in the circuit of said sluggish relay and controlled by the test-relay, a source of ringing-current, a relay (1 controlled from the substation adapted to connect said source with one of the brushes when relay is becomes energized, a locking-winding for the test-relay, and a circuit for said winding controlled jointly by said relay 0 and the test-relay; whereby if the wanted line is busy the test-- relay is operated to open the circuit of relay 7: and apply busy-test current to the callingline, but if the called line is free, relay 7c is en ergized, connecting the brushes with the call ing-line, disconnecting the test-relay from the switch-arm, and permitting relay a to apply ringing-current to said brush.

In witness whereof I hereunto subscribe my name this 19th day of July, A. D. 1905.

ALBERT M. BULLARD.

Witnesses:

J. H. FOWLER, H. S. MAGUIRE.

a." aMpMaeuhas... 

